1. Field of the Invention
The invention relates to a hybrid vehicle and a control method thereof.
2. Description of the Related Art
A conventional hybrid vehicle includes an engine, a planetary gear mechanism including a planetary gear that is connected to a crankshaft of the engine, a first motor connected to a sun gear of the planetary gear mechanism and capable of generating power, a second motor capable of outputting power to a ring gear shaft that serves as a drive shaft connected to a ring gear of the planetary gear mechanism, and a battery capable of exchanging power with the first and second motors (see Japanese Patent Application Publication No. 2003-32805 (JP-A-2003-32805), for example). In this hybrid vehicle, when an abnormality occurs in a second central processing unit (CPU) that controls the second motor, the second motor is controlled by a first CPU that controls the first motor, and therefore both the first and second motors can be driven to execute evasive travel when an abnormality occurs.
In a hybrid vehicle such as that described above, when an abnormality occurs in the engine or in a sensor, an accessory or the like related to the engine while the engine is operative, as long as the second motor and accessories related thereto are normal, the hybrid vehicle can be allowed to continue traveling by gate-blocking an inverter that drives the motor MG1 such that the engine is stopped and power is output to the drive shaft from the second motor. However, when the engine is stopped suddenly due to an abnormality relating to the engine while the engine is operative and the hybrid vehicle is traveling at a comparatively high speed, a rotation speed of the engine may decrease more rapidly than the vehicle speed, while respective rotation speeds of the sun gear of the planetary gear mechanism and the first motor connected thereto may increase rapidly in an opposite direction to a previous direction. As a result of these sudden rotation speed changes, a problem, or in other words a secondary malfunction, may occur in the planetary gear mechanism and so on, which have been operating normally up to this point.